Calendrical software
Some calendars are sufficiently simple that their use requires no more calculation than can be done mentally. An example is the Gregorian Calendar, whose use requires nothing more complicated arithmetically than division of a year number by 400 (even though the rule for leap years is sufficiently complex that many people cannot understand it without mental effort). To determine the structure (of years, months, days, etc.) of a calendar it may be necessary to use complex calculations. An example is the Chinese Lunar Calendar, which requires an exact determination of the time of the dark moon at a particular longitude. The Chinese Calendar was invented over 2000 years ago, long before there were any computers in the modern sense of the term, so clearly a computationally intensive calendar can be developed and used without reliance on modern computers. But these days computation is indispensible in the study of calendars. This computation is of two kinds: That required simply to compute the structure of a calendar, and that required for more scholarly studies (for example, the extent to which new years day in a solar calendar varies with respect to one of the seasonal markers, in particular, the vernal equinox. This article discusses calendrical software of the first kind only. The obvious way to classify calendrical software of this kind is in terms of the calendars that it deals with. Some software, of course, handles dates in more than one calendar, so in what follows there is some duplication. In each of the calendars listed a distinction is made between software which is written for the PC, the Macintosh, some other system, or whether the software is a web application. Some of this software is free and some is try-before-you-buy (the name of the software publisher is given after the title). There are a couple of additional sections not concerned with specific calendars, such as software for calculating the dates of solstices and equinoxes. Annus Novus Decimal Calendar Arithmetic Operations on Calendar Dates Armenian Calendar DOS (Windows console applications) *Armenian Calendar Gerhard Behrens Aztec Calendar Web applications *Aztec Calendar Converter René Voorburg, William Horden and Marta Ramirez ' Chinese Lunar Calendar Common Era Calendar (Gregorian Calendar) Easter date Goddess Lunar Calendar Hebrew Calendar '''Web applications' *Calendar Converter John Walker Hermetic Leap Week Calendar Hermetic Lunar Week Calendar The Hermetic Lunar Week Calendar specifies days by means of dates of the form year-month-week-day, where a year has 12 or 13 months, a month has exactly four weeks, and a week consists usually of 7 or 8 days but sometimes of 6 or 9 days. Weeks track the lunar quarters exactly. Windows software *Lunar Calendars and Eclipse Finder Hermetic Systems Web applications *Printable Hermetic Lunar Week Calendar Hermetic Systems *Hermetic Lunar Week Calendar Day Count Hermetic Systems Islamic (Hijri) Calendar Web applications *Calendar Converter John Walker ISO Week Calendar The ISO Week Calendar is a leap week calendar that is used mainly in government and business for fiscal years. It uses the conventional 7-day week, with weeks starting on Monday. Years begin within 3 days of the start of the Common Era Calendar year, and each year has exactly 52 or 53 weeks. There is not a lot of off-the-shelf software for conversion of dates in the ISO Week Calendar. Windows software *Easy Date Converter Hermetic Systems Web applications *The ISO Week Date Calendar Rick McCarty Japanese Calendar Julian Calendar Web applications *Calendar Converter John Walker Julian Day Number The Julian day number system is not itself a calendar, but is of central importance in the study of calendars. This system sets up a one-to-one correspondence between days (more exactly nychthemerons) as observed on Earth and the integers: ..., -2, -1, 0, 1, 2, 3 ... This allows identification of a particular day without reference to any particular calendar. An informal definition of the Julian day number is: The number of days elapsed since ‑4712-01-01 JC, that is, since January 1st, 4713 BCE in the Julian Calendar. It can also be defined as: The integral part of the astronomical Julian date at 12 noon GMT on that day. For example, the Julian day number of 2007-02-23 CE is 2,454,155. The software listed below supports conversion of dates in various calendars to and from Julian day numbers. Windows software *Chinese Calendrics Hermetic Systems *Easy Date Converter Hermetic Systems *Julian Day Converter Gedesoft *Lunar Calendars and Eclipse Finder Hermetic Systems *Mayan Calendrics Hermetic Systems *Trayday MJMSoft Design Web applications *Monthly Calendar & Julian Date Calculator 1728 Software Systems *Calendar Converter John Walker Kalacakra Calendar The Kalacakra Calendar is a solilunar calendar in which days are numbered according to the Moon's longitude. DOS (Windows console applications) *Kalacakra Calendar Software Edward Henning Liberalia Triday Calendar Lunar and Solar Eclipses Maya Calendar The Maya used three different calendrical systems (and some variations within the systems). The three systems are known as the tzolkin, the haab and the long count. The tzolkin is a cycle of 260 days and the haab is a cycle of 365 days. Since the Maya calendar is fairly complex, the need for software to handle dates in this calendar has long been recognized. Note that there is still some uncertainty regarding how dates in the Maya Calendar should be correlated with dates in the Common Era Calendar (this is known as the correlation problem). Thus all Maya Calendar software which converts Maya dates into European dates should have some way to set the so-called correlation number. Windows software *Maya Calendar Program Xoc Software *Mayan Calendrics Hermetic Systems Web applications *Maya Calendar Dawn Jenkins & Michiel Berger *Pictographic Maya Calendar Converter C. Hartley *Calendar Converter John Walker Meyer-Palmen Solilunar Calendar The Meyer-Palmen Solilunar Calendar has dates in the form cycle-year-month-day where each cycle consists of 60 years. Most years have twelve months, but some have thirteen. Windows software *Lunar Calendars and Eclipse Finder Hermetic Systems Ordinal (Day-in-Year) Dates Persian (Jalali) Calendar Solstices and Equinoxes Symmetry454 Calendar *Kalendis Calendar Calculator Irv Bromberg Tibetan Calendar There is no Tibetan Calendar software at present which converts between Tibetan and Western dates because the exact calculational principles used by the Tibetan calendar makers from year to year has not been made public. There is, however, a web application for converting between Tibetan and Western years. Web applications *Tibetan Calendar Converter Fred Coulson Tabot Calendar The Tabot Calendar is a Rastafarian calendar related to the Common Era Calendar. Web applications Today's date in the Tabot Calendar Vietnamese lunar calendar Web applications *Vietnamese lunar calendar Ho Ngoc Duc